Is it possible for a four tube amp to operate with only 1 tube?

Discussion in 'Glowing Bottle Tube Amp Forum' started by 3-Chord-Genius, May 24, 2020.

  1. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    I ask because I just saw an interview with the engineer who worked on In Utero (Nirvana) and he specifically stated that Kurt Cobain had decided to use different amps for different songs on that album, and for this song he used a Fender 4-power tube amp with three missing tubes:




    Here's the interview. Go to 9:05.

     
    Last edited: May 25, 2020
  2. pedalcr8z

    pedalcr8z Tele-Meister

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    Not likely as at a bare minimum it would need at least 1 preamp and 1 power amp tube and that's only if it has solid state rectification.
     
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  3. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    I was thinking a push-pull amp would need to do both in order to do anything. With only one tube it's either a-pushin' or a-pullin'.
     
  4. Mexitele Blues

    Mexitele Blues Tele-Holic

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    You can remove 4 preamp tubes from a Fender Twin and still play the normal channel.
     
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  5. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    The amp the guy in the video was talking about apparently only had one *power* tube out of four...
     
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  6. Mexitele Blues

    Mexitele Blues Tele-Holic

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    Interesting claim. I have no idea.
     
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  7. pedalcr8z

    pedalcr8z Tele-Meister

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    deleted
     
    Last edited: May 25, 2020
  8. BobbyZ

    BobbyZ Doctor of Teleocity

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    Yeah a Twin Reverb will work with just one 6L6 power tube. However it makes an amp designed to run class AB push pull run class A single ended. If that would hurt it with long term use I really don't know? I do it sometimes to find a weak tube and I'll do it in two power tube amps for the same reason. But that's only a few minutes.
     
  9. koolaide

    koolaide Tele-Holic

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    I am no expert, but as I understand it, It would run with a preamp and a power tube, but would likely damage the amp due to over voltage and bias issues. How long it would run before being damaged or burning up a tube(s) I can't say. Cleary IMHO not a good idea. Maybe OK tor troubleshooting as BobbyZ does it for only a few minutes. YMMV.
     
  10. dogmeat

    dogmeat Tele-Afflicted

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    answer to the original question is... no.
     
  11. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    I was wondering about this. I know you can pull two apposite tubes from a quad and it will run at half-power, but I always assumed there had to be a pair in there at least in order for it to be able to run. I'd like to know the background of the particular amp in the video because reportedly Cobain liked the sound with only one tube enough to bring that amp to a studio, so it must have been somehow working long enough for him to decide that he liked the sound beforehand.
     
  12. robrob

    robrob Poster Extraordinaire Ad Free Member

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    ^What BobbyZ said. With 3 out of 4 power tubes pulled the amp will play and sound surprisingly good. The first time I found a completely dead power tube in a 2x6V6 amp I was stunned at the tone and volume it put out.
     
  13. BobbyZ

    BobbyZ Doctor of Teleocity

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    I've ran into several dual power tube amps that for one reason or the other were only running on one power tube. These days with low gig volumes and so much home playing the owners often don't even know there's even a problem.
     
  14. Dacious

    Dacious Poster Extraordinaire

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    One day I turned up to practice with my 78 Princeton Reverb and it was sounding dull and lacking volume. As I tilted it over to check it out I heard a 'tink' and a tube rolled in the bottom.

    One power tube has dropped out due to loose clinches in the socket. Modern tubes in vintage amps can do that due to skinny pins and sloppy index key. It seemingly had no problem running, showed no evident sign of distress. I plugged the tube back in and it operated as normal.

    I couldn't imagine recording with it - it sounded flat.
     
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  15. hepular

    hepular Tele-Meister

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    watched a couple of these, think it was a showman that according to albini, everyone else thought it sounded horrible, but cobain liked it BECAUSE it sounded awful.

    barely related is this story from the comments to this video:

    A little behind the scenes info. During the day of this show, Nirvana rolled up to FMC Associates in Watertown, CT at 12:00 pm. They had a dead Ampeg SVT bass head, brought to US to fix. We had to overnight parts etc to fix it. Meantime the band was hanging out in our shop till we could locate from the music Stores we did repairs for a bass Amp for them to rent for the Moon show. We located a new Ampeg SVT from Brian Guitars on Amity rd in New Haven however he wouldn't rent to them! (afraid never see it again). So we rented in our shops name and paid Brian's telling the band we would add it to there bill. Curt was so positive about things then. He was telling us they where going to be really big. He gave us an original copy of SLTS with the original cover. Dave was just mellow, mostly practicing on a pillow in our lounge. Don't remember much about Chris that day. My Partner Rich followed the bus down to New Haven to get the amp head from Brian's. Then went to the Moon. U had to stay to close the shop do I never went. Next day we finished the repair on Chris's Amo head and the once again came back to FMC to get it. The bill with all the charges was around $300 . Kurt happily Wrote us a check from their tour support account. We said goodbye and the band was off. I guess Brian's was right about renting to them. That check bounced, a further testament that tour lost money! Great to finally see the show I missed!
    Show less
     
  16. RoyBGood

    RoyBGood Doctor of Teleocity

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    Unless there were undisclosed internal mods that allowed the lone tube to operate in single-ended / class A mode, like a VHT Special 6 Ultra, I can't see that being true.
     
  17. Wally

    Wally Telefied Ad Free Member

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    A push/pull amp will function with only half of the output transformer primary involved, but it will create only half of the sine wave....the top or the bottom depending on what tube/s are pulled.
    It will not sound as it was designed to sound. Whether one likes the result is a personal thing, but IF Cobain liked the results for that application because the amp sounded terrible, then imho And ime he was making an aurally informed choice to use a compromised circuit to get some trash sound.
    Think about this......a 6 cylinder engine will run with one cylinder dropped out....it just won’t do what it was designed to do.
     
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  18. Ten Over

    Ten Over Tele-Holic

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    Only if it is biased for class B. For class AB1 biasing, both sides of a sine wave will be created until the tube hits cut-off. Sort of like a cold-clipper.
     
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  19. Wally

    Wally Telefied Ad Free Member

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  20. MuddyWolf

    MuddyWolf Tele-Meister

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    Tubes in a tube amp? What makes you think you need those? It's just a scam rock star's pull to keep young players down and soak up all your lawn mowing money. Save money and use old Christmas lights bulbs. The red ones work the best.
     
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